A daylighting layer for collecting solar light into indoors through a window or the like of a building is proposed in PTL 1. In the daylighting layer, a plurality of unit prisms and a flat surface are formed in one surface of a support with optical transparency. The solar light is collected indoors through the unit prism. By disposing such a daylighting layer to a window glass, a bright space can be provided by introducing external light indoors.
In recent year, from the viewpoint of energy conservation, there are required for improving of heat insulating properties in the window portion. Since the above-described daylighting layer is used in a state where the daylighting layer is attached to an indoor side of the window glass, the heat is also entered indoors in addition to external light. As a result, there is a problem in that unnecessary air-conditioning cost is generated due to the heat in summer season.
As a test for improving the heat insulating properties of the window portion, improving the heat insulating properties by disposing the double window glasses is well known. In NPL 1, a configuration, in which a daylighting layer is disposed between two window glasses which are disposed facing each other, is proposed.